The feeding systems currently used are mostly of the following types:
a--For annual plants: PA1 Truncated or variable pitch continuous screws provided at the extremity of a counter-pressure system. The system makes it possible to avoid any flowing back of the material by means of the vapor pressure, generally about 7 bars, existing inside the cooker. PA1 These screws have a certain number of drawbacks, namely rapid wear owing to the presence of silica in the plants used (cane trash, gambo fiber, straw, hemp, etc), which requires the screws to be changed frequently (for recharging with metal) and, for certain plants (especially humid straw), resulting in rendering it difficult to ensure a regular flow owing to the fact that the material tends to rotate with the screw and move no further. PA1 This drawback adversely affects the quality of the pulp obtained and thus reduces the productivity of the installation. PA1 b--For wood chips, the systems used are rotary valve or sieve type systems. These devices function according to the following cycle: PA1 1. A certain quantity of chips is introduced into a volume at atmospheric pressure. PA1 2. The volume is closed and subjected to a vapor pressure equal to that of the cooker. PA1 3. The volume is opened towards the cooker and the chips are dumped from the cooker. PA1 4. The volume is closed again and then held at atmospheric pressure. PA1 a) mixture of the impregnation solution in proportions required for cooking by means of conventional agitation, and PA1 b) submission of this mixture when being introduced into the cooker to a high pressure, preferably about 80 bars, by means of compression with the aid of an open yoke piston pump, which forces the impregnation solution to penetrate into the lignocellulose material.
The volume is then ready to receive a new load of chips.
Such systems exhibit drawbacks as they are discontinuous and accordingly disturb the functioning of the cooker and bring about a head loss on each cycle.